1. Field of the Invention
The invention concerns an insertion instrument for an endoprosthesis, comprising a neck part and a shaft part which is to be inserted into a medullary cavity, whereby the instrument comprises a clamping device with a holding fork and a thrust bearing, which are designed to maintain the prosthesis shaft in a clamped state and to release it in an unclamped state and also comprises a striker device.
2. Description of the Related Art
In order to join endoprostheses to the end of a tubular bone such as the femur, usually prosthesis shafts are provided which are introduced into a medullary cavity of the tubular bone. For this purpose, during the implantation of the prosthesis, the medullary cavity has to be opened, its inside removed to the required extent, and finally the shaft of the prosthesis is to be inserted. In order to achieve a solid and secure positioning of the prosthesis shaft in the tubular bone, the cavity to be created in the medullary cavity has to be adjusted to the contour of the shaft in order to be inserted as accurately as possible. Subsequent corrections of the position of the prosthesis shaft lead to widening of the cavity and thus to a less secure seat. The long-term stability of the prosthesis is thereby endangered. This applies especially when the implantation of the endoprosthesis is to be done without any cement.
Various instruments have become known with which the prosthesis can be implanted with its shaft. An insertion instrument is known from EP B 0 852 931, which has a grip part with a coupling onto which a rasp can be arranged for clearing the cavity in the medullary cavity or on which the shaft of the endoprosthesis to be inserted can be arranged. The rasp is designed as a profile rasp and serves to form a cavity corresponding to the contour of the shaft to be inserted. Once the cavity is created, the rasp can be removed from the grip end and the shaft of the endoprosthesis can be connected to the grip part. A similar insertion instrument is known from EP B 0 956 824. The grip part has a remote-controllable quick coupling, with the aid of which the rasp or the prosthesis shaft to be inserted is held on the grip part. Furthermore, on its back end away from the coupling, the grip part has an anvil. This serves as striking head. With this, when the shaft fits tightly in the medullary cavity, the endoprosthesis can be driven into its final position by hammer strokes.
A disadvantage of the insertion instruments of the state of the art lies in the fact that position changes, as they occur especially in the case of corrections, lead to a widening and thus to a worsening of the seat of the shaft in the medullary cavity of the bone. This applies especially when corrections are first made at the time of the hammering in. Moreover, it may occur inadvertently that due to difficult access conditions, the hammer strokes are done in an unfavorable direction onto the striking head. As a result of this, not only incorrect positioning of the shaft and thus of the prosthesis with respect to the bone occurs, but also the poorer seat would lead to the danger of premature loosening.